I use both. Still life stuff and landscapes are best with a tripod, but even a lot of my landscapes are impulse images and that's where the Is (mine is in the camera body of my Pentax Dslr) allows sharp images. I have no really long lenses but my zoom goes to 300 (450equivalent)and the built-in Anti-shake does wonders.

I really don't think it's a question of one or the other. Both are necessary additional tools for us.